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Search: id:A006254
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| A006254 |
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Numbers n such that 2n-1 is prime. |
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+0
31
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| 2, 3, 4, 6, 7, 9, 10, 12, 15, 16, 19, 21, 22, 24, 27, 30, 31, 34, 36, 37, 40, 42, 45, 49, 51, 52, 54, 55, 57, 64, 66, 69, 70, 75, 76, 79, 82, 84, 87, 90, 91, 96, 97, 99, 100, 106, 112, 114, 115, 117, 120, 121, 126, 129, 132, 135, 136, 139, 141, 142, 147, 154, 156, 157
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The following sequences (allowing offset of first term) all appear to have the same parity: A034953, triangular numbers with prime indices; A054269, length of period of continued fraction for sqrt(p), p prime; A082749, difference between the sum of next prime(n) natural numbers and the sum of next n primes; A006254, numbers n such that 2n-1 is prime; A067076, 2n+3 is a prime. - Jeremy Gardiner (jeremy.gardiner(AT)btinternet.com), Sep 10 2004
Also, odd primes plus 1, divided by 2: a(n)=(1 + A065091(n))/2. - O. E. Pol (info(AT)polprimos.com), Nov 10 2007
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..1000
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FORMULA
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a(n) = (A000040(n+1) + 1)/2 = A067076(n-1) + 2 = A086801(n-1)/2 + 2.
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MATHEMATICA
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Rest@Prime@Range@70/2 + 1/2 (from Robert G. Wilson v (rgwv(at)rgwv.com), Jun 16 2006)
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CROSSREFS
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Cf. A000040, A067076, A086801.
Equals A005097 + 1. A130291 is an essentially identical sequence.
Cf. A065091.
Sequence in context: A047301 A001953 A079057 this_sequence A111333 A047701 A127963
Adjacent sequences: A006251 A006252 A006253 this_sequence A006255 A006256 A006257
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KEYWORD
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nonn,easy
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AUTHOR
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Marc LeBrun (mlb(AT)well.com)
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EXTENSIONS
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More terms from Erich Friedman (erich.friedman(AT)stetson.edu).
More terms from O. E. Pol (info(AT)polprimos.com), Nov 10 2007
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